Stripping a solution containing molybdenum and vanadium values

ABSTRACT

A method of stripping an organic extraction solvent containing quaternary alkyl ammonium complexes. The extraction solvent is contacted with an aqueous stripping solution having at least 75 g/l bicarbonate ion, while maintained at between pH 7 and 9 at a temperature of no more than 50° C.

BACKGROUND OF THE INVENTION

This invention relates to methods of stripping extracted constituentsfrom organic extractants. More particularly, this invention relates tomethods of stripping constituents from quaternary amine extractants.

A number of important hydrometallurgical processes involve theextraction of metal species in the form of anionic metal complexes fromaqueous pregnant liquors, and subsequent stripping of the metal valuesfrom the organic phase into an aqueous phase. Such extracting andstripping processes are especially important in the hydrometallurgy ofGroup V and Group VI metals. One particularly important source ofaqueous pregnant liquors containing both Group V and Group VI metalvalues is the pregnant liquor produced from leaching spenthydroprocessing catalysts.

The chemistry of Group V and Group VI metals in aqueous solution isparticularly complex. Each metal in both Groups forms a variety ofoxidation states that can in turn form a variety of oxygen-containinganions in aqueous solution. These metal-oxygen complexes undergo complexreactions in aqueous solution that depend on such variables as pH,temperature, concentration and chemical environment. Each metal of theGroup V and Group VI undergoes reactions at unique conditions. Thecomplex aqueous chemistry of Group V and Group VI metals makes theliquid-liquid phase transfer processes particularly difficult,especially if more than one metal species of Group V and Group VI arepresent.

Crude oils frequently contain metals, particularly iron, nickel andvanadium. Spent hydroprocessing catalysts that have been in contact withmetals containing crude or residual oil can therefore contain bothmolybdenum, a frequent catalytic metal, and vanadium. Extracting andstripping the vanadium values and the molybdenum values simultaneouslyfrom a leach liquor from spent catalysts therefore presents a difficultand subtle problem.

It is preferred, that if the metals from catalysts are to be recoveredby hydrometallurgical techniques, that the total flow scheme be one thatallows maximu recycle of reagents and minimum introduction of extraneousions. Since one preferred recovery system involves an aqueous ammoniacalleach using ammonium carbonate, it is preferred that only ammonia,ammonium ion or carbonate ion be added to the aqueous streams. Thisself-imposed limitation complicates the recovery scheme of Group V andGroup VI metals even more.

It is possible, at pH values in the range of about 3 to about 5, toextract both molybdenum and vanadium into an organic phase by use of aquaternary amine as a liquid anion exchange reagent. One such reagent istricapryl methyl ammonium chloride, which is sold under the trade nameAlaquat 336® by the Henkel Chemical Company.

Alaquat and related compounds that have extracted constituents fromGroup V and Group VI on them tend to be difficult to strip, especiallyif the strip is to be chemically compatible with the leach. In U.S. Pat.No. 3,083,085 an aqueous solution of NaCl is used to strip molybdenumfrom the organic phase. This requires regeneration of the organicextracting solution with sulfuric acid and the use of expensive alloysin process equipment that are not corroded by chloride ion.

U.S. Pat. No. 3,083,076 discloses the use of an aqueous solution of bothsulfate and sodium hydroxide to strip molybdenum and vanadium from theorganic solution. Again, this strip is chemically incompatible with theleach and requires corrosion resistant process equipment.

It has been discovered that an aqueous solution or bicarbonate anion isparticularly effective for stripping both Group V and Group VI metalsfrom organic solutions containing quaternary ammonium compounds.Bicarbonate provides high recoveries under mild conditions and ischemically compatible with the ammonical leach step in an overallprocess to recover metal values from spent hydroprocessing catalysts.

SUMMARY OF THE INVENTION

This invention provides a method of stripping an organic extractionsolvent containing metal quaternary alkyl ammonium complexes. Theorganic extraction solvent is contacted with an aqueous strippingsolution maintained at a temperature of no more than 50° C., and havinga pH of between 7 and 9, and containing at least 75 grams per liter of asalt of a bicarbonate ion, for a time sufficient to convert the metalquaternary alkyl ammonium complexes to aqueous soluble metal complexes.The organic extraction solvent and the metal containing aqueous stripsolution are then separated.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a flow scheme for an embodiment of this invention.

FIG. 2 shows in detail the flow scheme of this invention.

FIG. 3 shows Raman spectra of several solutions including two containinga new vanadium complex.

DETAILED DESCRIPTION

As world oil reserves dwindle, more heavy oil, with high concentrationsof metals and sulfur, must be refined. One process, in the refining ofsuch metals containing oil, is to contact with hydroprocessing catalyststo remove metals and sulfur. After a period of time, these catalysts donot give desired product quality and must be replaced. These usedcatalysts are herein defined as spent catalyst. Spent catalysts, fromdemetalation service, have relatively high amounts of metals depositedon their surface and also contain catalytic metals.

Metals recovered from crude oils are typically iron, nickel, andvanadium, and catalytic metals are generally molybdenum and cobalt ornickel. The metals can be leached simultaneously from spent catalystthat has been roasted to remove carbonaceous and sulfurous residues. Anexcellent leach system for spent catalyst is an aqueous solution ofammonia and ammonium salt. The pregnant liquor from the leach can bedivided into two fractions: an aqueous solution of amine complexes ofthe cationic metals, nickel and cobalt, and an aqueous solution ofanionic metal oxide ions, molybdates and vanadates.

If both molybdenum and vanadium are present, they can be removedtogether by liquid-anion exchange extraction techniques, usingquaternary ammonium compounds as the extracting agent. By use of thepresent invention both metals can be extracted and strippedsimultaneously. The individual metals can then be separated in latersteps providing highly pure concentrates or crystalline materials.

The quaternary ammonium compounds of this invention can be made by thegeneral method of U.S. Pat. No. 3,083,085.

In addition to the quaternary ammonium compound, the organic phasegenerally includes other materials such as a conditioner which typicallyis a long chain aliphatic alcohol such as capryl alcohol, decanol,tridecyl alcohol or 2-ethyl hexanol, and a diluent such as kerosene orhigh flash point fuel oils. The composition of the organic phase is notcritical, but is generally preferred that it consists of from 5 to 15volume percent quaternary ammonium compound, 2 to 10 volume percent ofconditioner with the remainder being kerosene or fuel oil.

The stripping agent of this invention is bicarbonate, preferablyammonium bicarbonate. It has been found that singly charged anions inthe aqueous strip solution remove metals more completely than anionswith larger charge. Since bicarbonate is the singly protonated form of apolyprotic acid, pH control of the strip solution becomes critical. Thepreferred pH range is 7 to 9, more preferably 7.5 to 8.5.

The preferred stripping salt is ammonium bicarbonate, a temperaturesensitive compound that can easily degrade to ammonia, carbon dioxide,and water. It has been found that, in the system of the presentinvention, stripping of the loaded organic solution is favored at lowertemperatures. It is preferred that the temperature never go above about50° C. and more preferably that the temperature not go above 25° C.

Bicarbonate ion will be present in at least 100 grams per liter andpreferably in at least 75 grams per liter in the stripping solution. Itis known that the more concentrated the stripping agent in the strippingsolution, the more metal is extracted. Therefore, the optimumconcentration for the practice of this invention is saturation. Thestripping solution will be in contact with the organic for a period oftime sufficient to convert the metal quaternary alkyl ammonium complexesin the organic solution to aqueous soluble metal complexes. The twosolutions are then separated by means known in the art.

One advantage of using ammonium bicarbonate is that the ammonia andcarbon dioxide constituents can be easily evaporated and recycled metaloxide. In an overall process using an aqueous ammoniacal and an ammoniumcarbonate leach where the organic reagent is circulated back to extractfresh metal, the use of bicarbonate does not foul the metal-free leachliquor with extraneous anions.

An interesting feature of stripping vanadium containing Alaquat® is theformation of a unique chemical species unreported in the literature. Thestrip solution of an organic solution that contains vanadium has acharacteristic light green color. This color is not due to any vanadiumcomplex that is known to exist at these conditions.

The Raman spectrum provides further evidence of the unique character ofthis complex.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 illustrates an embodiment of this invention. Shown is a totalflow scheme for recovering metals from spent catalyst known to containcobalt, nickel, molybdenum and vanadium. The catalyst is first roastedunder conditions where the temperature is controlled to less than 600°C. The spent roasted catalyst is then leached at 90° C., until cobaltvalues in solution start to decrease. The pregnant liquor is thenextracted with a quaternary amine, forming a first set of two streams:an organic stream containing molybdenum and vanadium, and an aqueousstream containing cobalt and nickel. The first organic stream isstripped by the process of this invention with an aqueous solution ofammonium bicarbonate. Hydrochloric acid is added to the aqueous stripsolution and ammonium metavanadate is precipitated. The volume of thesolution is reduced and ammonium molybdate is precipitated.

Excess ammonia is removed from the first aqueous stream, by heating thesolution. The solution, which is exposed to air insuring that cobalt isin the trivalent oxidation state, is extracted with LIX 64N®, removingthe nickel and creating a second set of two streams: an aqueous,containing cobalt and any impurities and an organic containing nickel.The second organic solution is stripped with sulfuric acid, forming anacidic nickel containing sulfate solution. The cobalt in the secondaqueous stream is reduced over cobalt shot, and extracted with LIX 51®,thereby forming a third set of aqueous and organic streams.

The third aqueous stream is recycled to the leach step, enriched inammonia removed from the ammonia distillation step. The third organicstream is stripped with solution of a solution of ammonia and ammoniumcarbonate.

FIG. 2 shows another embodiment of the strip of this invention. Anaqueous solution containing metal ions, including Group V and Group VImetal oxide anions, is contacted with a quaternary ammonium liquid anionreagent. The resulting organic metal containing solution is stripped byan aqueous solution of ammonium bicarbonate. The stripped organicsolution can then be recycled without having had any extraneous ionsplaced into it by the strip solution. The result is an aqueous metalsolution containing both the Group V and Group VI metal values.

FIG. 3 shows four Raman spectra. Spectrum A is that of an aqueoussolution of 5 g/l V, as NaVO₃ at pH 8.8. The transition states wereassigned as follows:

                  TABLE 1                                                         ______________________________________                                        Transition                                                                    Energy (cm.sup.-1)                                                                        Intensity      Assignment                                         ______________________________________                                        1047        VS             NO.sub.3.sup.-                                     987         W              H.sub.x V.sub.10 O.sub.28.sup.(6-x).spsp.-         947         VS             (VO.sub.3.sup.-).sub.n                             713         VW             NO.sub.3.sup.-                                     629         VW             HCO.sub.3.sup.-                                    362         W              VO.sub.3.sup.-                                     319         W              VO.sub.3.sup.-                                     ______________________________________                                    

where VS is very strong, S is strong, M is medium, W is weak and VW isvery weak.

Spectrum B is that of an aqueous solution of 5 g/l V and 68 g/l NaHCO₃at pH of about 8.8. The transition states of this solution, believed tobe those of a new unreported vanadium complex were assigned as follows:

                  TABLE 2                                                         ______________________________________                                        Transition                                                                    Energy (cm.sup.-1)                                                                        Intensity  Assignment                                             ______________________________________                                        1064        M          CO.sub.3.sup.2-                                        1046        VS         NO.sub.3.sup.-                                         1014        VS         HCO.sub.3.sup.-                                        923         VS         V (V) carbonato complex                                718         VW         NO.sub.3.sup.-                                         675         VW         CO.sub.3.sup.2-                                        625         VW         HCO.sub.3.sup.-                                        489         VW         glass                                                  435         M          V (V) carbonato complex                                354         W          V (V) carbonato complex                                ______________________________________                                    

Spectrum C is that of an aqueous solution of 68 g/l Na₄ /CO₃. Thetransition states were assigned as follows:

                  TABLE 3                                                         ______________________________________                                        Transition                                                                    Energy (cm.sup.-1)                                                                         Intensity      Assignment                                        ______________________________________                                        1063         M              CO.sub.3.sup.2-                                   1049         VS             NO.sub.3.sup.-                                    1016         VS             HCO.sub.3.sup.-                                    672         VW             CO.sub.3.sup.2-                                    629         VW             HCO.sub.3.sup.-                                   ______________________________________                                    

Spectrum D is that of an aqueous strip solution in pilot plant use ofthe present invention. The solution contained about 5 g/l V and 200 g/lammonium bicarbonate. The transitions were assigned as follows:

                  TABLE 4                                                         ______________________________________                                        Transition                                                                    Energy (cm.sup.-1)                                                                       Intensity                                                                              Assignment                                                ______________________________________                                        1063       M        CO.sub.3.sup.2-                                           1019       VS       HCO.sub.3.sup.2-                                          917        VS       Vanadium V carbonate complex                              888        sharp    ?                                                         674        W        CO.sub.3.sup.2-                                           633        W        HCO.sub.3.sup.-                                           438        M        Vanadium V carbonato complex                              347        W        Vanadium V carbonato complex                              ______________________________________                                    

EXAMPLE 1

This example shows the affect of varying bicarbonate concentrations inease of stripping metals from a solution of 10% Aliquot in 10% decanoland kerosene loaded with both molybdenum and vanadium. Aqueous solutionhaving the following concentrations of NH₄ HCO₃ were made: 6.84, 13.68,20.52, 100.0 and 200.0 grams per liter. An aqueous to organic ratio of1:1 was used for all concentrations.

The results of the experiments are tabulated in Table 5.

                                      TABLE 5                                     __________________________________________________________________________           INITIAL FINAL       INITIAL FINAL                                      [NH.sub.4 HCO.sub.3 ]                                                                   Mo*  Mo             V*   V                                          g/l    pH org(g/l)                                                                           org(g/l)                                                                           aq(g/l)                                                                           pH pH org(g/l)                                                                           org(g/l)                                                                           aq(g/l)                                                                           pH                                __________________________________________________________________________    6.84    8.29                                                                            3.3  2.9   0.26                                                                             8.73                                                                             8.29                                                                             6.3  6.132                                                                              0.025                                                                             8.62                              13.68   8.20                                                                            3.3  2.5   0.68                                                                             8.52                                                                             8.20                                                                             6.3  6.140                                                                              0.081                                                                             8.45                              20.52   8.20                                                                            3.3  2.1  1.1 8.42                                                                             8.20                                                                             6.3  6.010                                                                              0.182                                                                             8.36                              100.0   8.21                                                                            3.3  0.4  2.9 8.07                                                                             8.21                                                                             5.2  3.476                                                                              2.070                                                                             8.07                              200.0   8.34                                                                            4.0  0.3  3.7 8.41                                                                             8.34                                                                             5.2  1.247                                                                              3.360                                                                             8.45                              __________________________________________________________________________

Analysis for metal concentrations in solution was done by AtomicAbsorption.

EXAMPLE 2

Two organic solutions, one having 3.367 g/l of molybdenum loaded on 10%Aliquot in 10% decanol in kerosene, the other having 6.292 g/l vanadiumloaded onto 10% Aliquot in 10% decanol in kerosene, and two aqueoussolutions one with 20 g/l NH₄ HCO₃ and the other with 200 g/l NH₄ HCO₃were made up. A variety of organic aqueous ratios were chosen and theresults tabulated in Tables 6 and 7.

                  TABLE 6                                                         ______________________________________                                                20 g/l NH.sub.4 HCO.sub.3                                                                        200 g/l NH.sub.4 HCO.sub.3                         Ratio pH      org(g/l) aq(g/l)                                                                             pH    org(g/l)                                                                              aq(g/l)                            ______________________________________                                        15/1  8.97    3.019    1.389 8.70  2.517   9.412                              10/1  8.93    2.994    1.459 8.52  1.562   14.182                             5/1   8.87    3.189    1.540 8.35  1.036   11.871                             2/1   8.59    2.606    1.318 8.22  0.431   6.096                              1/1   8.40    2.217    1.097 8.09  0.248   3.315                              1/2   8.19     .570    0.808 8.02  0.151   1.743                              1/5   8.19    1.182    0.428 8.03  0.100   0.705                              1/10  8.19    0.660    0.266 8.00  0.119   0.350                              1/15  8.17    0.635    0.179 8.00  0.127   0.234                              ______________________________________                                    

Table 6 shows the data for stripping the Mo solution.

                  TABLE 7                                                         ______________________________________                                                20 g/l NH.sub.4 HCO.sub.3                                                                        200 g/l NH.sub.4 HCO.sub.3                         Ratio pH      org(g/l) aq(g/l)                                                                             pH    org(g/l)                                                                              aq(g/l)                            ______________________________________                                        15/1  9.03    6.412    0.162 8.52  5.228   *                                  10/1  8.97    6.306    0.175 8.35  5.326   *                                  5/1   8.6     6.144    0.179 8.32  3.850   *                                  2/1   8.44    6.080    0.177 --    2.310   *                                  1/1   8.53    6.104    0.178 8.10  0.743   5.700                              1/2   8.25    5.715    0.151 8.03          0.251                              1/5   8.17    5.690    0.137 8.00  0.186   1.112                              1/10  8.17    5.131    0.112 8.02  0.352   0.800                              1/15  8.20    5.050    0.100 7.99  0.277   0.385                              ______________________________________                                         *Precipitate Present                                                     

Table 7 shows the data for stripping V from the organic. One usualfeature of the 200 g/l NH₄ HCO₃ strip noted is a greenish color not inthe pregnant aqueous solution present in the 20 g/l NH₄ HCO₃ solution.It is suspected that this may indicate the formation of a previouslyunreported vanadium species.

EXAMPLE 3

This example shows the results of costripping both Mo and V from loadedorganic solvent with 200 g/l NH₄ HCO₃ solution. An organic solution wasprepared that had 3 g/l molybdenum and 6 g/l vanadium dissolved in akerosene solution containing 10% Aliquot and 10% decanol. Variousorganic to aqueous ratios were tried. The data is tabulated in Table 8.

                  TABLE 8                                                         ______________________________________                                        Ratio pH       org(g/l) aq(g/l) org(g/l)                                                                             aq(q/l)                                ______________________________________                                        15/1  8.49     0.168    *       5.175  *                                      10/1  8.51     0.077    *       4.226  *                                      5/1   8.52     0.104    *       4.664  *                                      2/1   8.29     0.051    *       2.166  *                                      1/1   8.16     0.030    *       0.750  *                                      1/2   8.01     0.015    0.083   0.321  3.048                                  1/5   8.03     0.008    0.034   0.234  1.305                                  1/10  8.00     0.007    0.016   0.211  0.603                                  1/15  8.00     0.012    0.011   0.349  0.393                                  ______________________________________                                         *an insoluble ppt formed                                                 

This example of the costrip of molybdenum and vanadium, shows theimportance of having an organic to aqueous ratio of less than 1:2 toprevent precipitation of metals containing species, thereby providingconveniently processed metal-containing solutions.

EXAMPLE 4

The greenish solution of Example 3 was analyzed by Raman spectroscopy.

Raman spectroscopy provides strong evidence for a vanadium V carbonatocomplexes. Tables 1-4 show the Raman bands of some vanadium containingsolutions and their assignment. All solutions were adjusted to pH 8.8using either nitric acid or sodium hydroxide. Sodium bicarbonatesolutions containing vanadium show an intense Raman band at 923 cm⁻¹ anda moderate bands at 435 cm⁻¹ and 354 cm⁻¹ as shown in FIGS. 3B and D.Neither vanadium-free sodium bicarbonate, FIG. 3C, nor bicarbonate-freemetavanadate solution, FIG. 3A, showed these bands. In addition, we havenoted that vanadium bicarbonate solutions usually have a characteristiclight green color which we suspect is due to the complex.

What is claimed is:
 1. A method of stripping an organic extractionsolvent containing molybdenum and vanadium quaternary alkyl ammoniumcomplexes comprising:contacting said organic extraction solvent with anaqueous stripping solution maintained at a temperature of no more than50° C., a pH of between 7 and 9, and containing at least 75 grams perliter of a salt of a bicarbonate ion, for a time sufficient to convertsaid molybdenum and vanadium quaternary alkyl ammonium complexes toaqueous soluble metal complexes; separating said organic extractionsolvent and said aqueous stripping solution.
 2. The process of claim 1wherein said salt of bicarbonate ion is ammonium bicarbonate.
 3. Theprocess of claim 1 wherein said organic extract solution containstri-caprylyl methyl ammonium chloride.
 4. The process of claim 1 whereinsaid bicarbonate concentration is at least 160 grams per liter.